Ionospheric absorption is usually obtained by subtraction
between decreased cosmic noise intensities due to absorption and background level of
cosmic radio noise in the absence of absorption (quiet day curve, QDC). Monthly QDC
is obtained in each month, using the inflection point method (IPM) proposed by
Armstrong et al. (1977). We developed properly the procession program of the QDC by
our group using the personal computer (Sato et al., 1992). Monthly QDC data are
stored in the QDC data file (for example, 91091200.QDC) of the PC.
Data file-name, scale of absorption value, and time-step are
printed at the head. Usually, the scale of 1 dB/div and time-step of 32 (128 sec
time-resolution) are used for quick-look data plots of absorption. As an example,
24-h absorption plots is printed for September 12, 1991 (91091200.NAL) (Figure 2). The 24-h plots present the absorption
variation for the eight beams (E1 to E8) along the N=4 column and for the eight
beams (N1 to N8) along the E=7 array. This 24-h plot data is useful for identifying
ionospheric absorption events and for estimating north-south and east-west movements
of absorption features.
